Non-reciprocal electric coupling device



June 5, 1962 G. DE VRIES 3,038,133

NON-RECIPROCAL ELECTRIC COUPLING DEVICE C0 U PIJNG FACTOR Filed Oct. 15,1957 l 250 300 MEGA c YCLES/SEC.

INVENTOR GERRIT DE VR ES BY W AGEfi:

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-; tates atent 3,038,133 Patented June 5, I962 This invention relates tonon-reciprocal electric coupling devices, in which the transmission ofenergy in one direction is nil.

Such devices are used, for example, as a microwave insulator, forexample in a connection between a generator and a load in order tosuppress the reaction of the load upon the generator. A plurality ofdevices of this kind are already known in which a piece of pre-polarizedhigh-frequency magnetic material, for example of ferrite, is arranged ata given area in a wave guide so that waves in the wave guide are passedsubstantially unhindered in one direction and materially damped in theother direction. However, such devices are not usable for comparativelylow frequencies, for example of the order of 500 mc./s., since thedimensions of the wave guide would become too large for practical use.

Furthermore, a non-reciprocal electric coupling device is already knownwhich comprises two crossing coils having their winding surfacesarranged at right angles to each other and surrounding a common core ofhigh-frequency magnetic material which is pre-polarized in a directionparallel to the intersecting line of the winding surfaces. Such acoupling device is indicated in certain cases by the name of gyrator. Insuch a gyrator, transmission of energy from one coil to the other may beeliminated by means of an external resistance coupling between the twocoils. In the reverse direction, however, transmission of energy cantake place. This device is not particularly suitable for waves having awavelength of the order of 50 cms.

The non-reciprocal electric coupling device according to the inventionlikewise comprises two crossing windings surrounding a common core ofhigh-frequency magnetic material which is pro-polarized in a directionparallel to the intersecting line of the winding surfaces. However, inthe device according to the invention, the winding surfaces are at anangle between and 90 and the prepolarization has a value such that for agiven frequency the transmission coeificient between the windings isnil. This device thus has no external coupling between the windings. Ifdesired, the windings may each comprise a single turn.

In order that the invention may be more readily carried into effect, itwill now be described more fully, by way of example, with reference tothe accompanying drawing.

FIG. 1 shows two crossing Lecher lines 1 and 2, which are eachshort-circuited at one end to form a single turn and which surround acore 3 of high-frequency magnetic material. The planes in which theconductors of the Lecher lines 1 and 2 are situated are at an angle of(p to each other. The core is pro-polarized in a direction parallel tothe intersecting line of said planes, as indicated by arrow H, by means(not shown), for example an electromagnet. Experiments have revealedthat an angle (p between 0 and 90 corresponds to a field strength H,with which at a given frequency there is no transmission of energy fromcoil 1 to coil 2, but such transmission is possible in the reversedirection.

FIG. 2 shows the relationship between the coupling factor S between thecoils 1 and 2 and the frequency f for different values H H H and H; ofthe pre-polarizing field. From the figure it may be seen that thecoupling factor S corresponding to the field strength H becomes nil fora frequency of 250 mc./s.

The foregoing may also be recognized theoretically as follows. Therelationship between the components Bxand By of the magnetic inductancein directions at right angles to the magnetic pre-polarization and thecorresponding components Hx and Hy of the magnetic field strength may ingeneral be expressed by the relations:

y=uz +m y wherein m and indicate complex permeabilities. From thecondition that the Lecher line 2 does not surround a magnetic fieldproduced by current in the Lecher line 1, it follows that tan (p must beequal to ,u iltz. From the fact that #1 and #2 are complex values, itfollows that two conditions must be fulfilled. The permeabilities a and[Q may approximately be expressed by the relations:

res

wherein 0: indicates the angular frequency, co the angular frequency atwhich for the given value of the prepolarizing field H magneticresonance of the high-frequency material occurs, and w the angularfrequency at which the magnetic material is in anti-resonance, that isto say at which the real part of the permeability ,u which indicates therelationship between a component of the mag netic inductance in adirection at right angles to the prepolarization and the component ofthe magnetic field in the same direction, is nil. In the above-mentionedformulae, ,8 indicates a magnitude which is proportional to the magneticlosses of the material, and j is equal to the root of 1. Uponsubstitution of the above-mentioned relations of ,u and 1. in thecondition tan p= #2 we have w=w and tan gr P es 2 ar ies From this itfollows that, in order to suppress transmission of energy from theLecher line 1 to the Lecher line 2, the pre-polarizing field for a givenfrequency to must be adjusted to a value such that the magnetic materialof the core 3- is in magnetic anti-resonance for this frequency.

What is claimed is:

A non-reciprocal electrical coupling device comprising a core ofhigh-frequency magnetic material, a first winding positioned to surroundsaid core and lying substantially in a first plane, a second windingpositioned to surround said core and lying substantially in a secondplane, said windings being oriented with respect to each other so thatsaid first and second planes intersect each other at an angle lyingbetween the values of zero and ninety degrees, and means forpre-polarizing said core in a direction parallel to the line ofintersection of said first and second planes, said pre-polarizationhaving a value to cause said core material to be substantially inmagnetic anti-resonance at a predetermined frequency whereby the signaltransmission coefiicient between said windings is substantially zero inone direction at said frequency determined by the value of saidpre-polarization.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Bloch et al. July 24, 1951 Hershber'gerMar. 18, 1952 Engelmann July 17, 1956 Anderson et a1. July 31, 1956 45Hogan July 2, 1957 Grisdale et al. May 13, 1958 FOREIGN PATENTS GreatBritain July 2, 1952 Great Britain Sept. 29, 1954

